25/26 U4: The Periodic Table and Atomic Structure

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Atom

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The basic unit of a chemical element.

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Atomic Model

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A theoretical model that describes the structure of an atom.

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Proton

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A subatomic particle found in the nucleus of every atom, carrying a positive charge.

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Neutron

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A subatomic particle found in the nucleus of atoms that is neutral, having no charge.

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Electron

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A subatomic particle with a negative charge, found in electron shells outside the nucleus.

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Nucleus

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The central part of an atom, containing protons and neutrons.

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Atomic Number

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The number of protons in the nucleus of an atom, determining the element's identity.

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Mass Number

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The total number of protons and neutrons in an atom's nucleus.

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Average Atomic Mass

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The weighted average mass of the atoms in a naturally occurring element.

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Periodic Table

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A table of the chemical elements arranged in order of atomic number.